In the field of ink jet printing, reaction liquids are used for improving print quality. The reaction liquid comprises a component that reacts with a component in the ink, e.g. the colloidal stability of dispersed pigment particles (present in the ink) is imparted by a metal salt (present in the reaction liquid). Therefore, upon contact between the ink composition and the reaction liquid, the dispersed pigment particles destabilize, agglomerate and are pinned to the print substrate. Therefore, (inter) color bleeding and coalescence on machine coated (MC) papers may be prevented, which is an improvement of the print quality. The optical density (OD) is increased and show-through is decreased on plain papers.
Reaction liquids are known from the prior art and usually comprise either a strong acidic compound or a (poly)valent metal salt, having the function of a fixer and/or crashing agent.
Reaction liquids, also termed reaction solutions, primer liquids, (pre-)treatment liquids or compositions, processing liquids or ink-receiving solutions, comprising polyvalent metal salts are known from the prior art, in particular from U.S. Pat. No. 6,419,352; U.S. Pat. No. 6,786,588; U.S. Pat. No. 8,523,342; U.S. Pat. No. 5,591,018; US 2011/0303113; US 2012/0098883; US 2012/0314000; and WO 2014/051547.
Published US Patent Application 2012/0019588 discloses fixer fluids, for ink-jet printing comprising a metal carboxylate salt as a fixer agent. In particular calcium acetate, calcium propionate, calcium butyrate, calcium bromide, calcium carbonate, calcium chloride, calcium citrate, calcium cyanamide, calcium phosphate, calcium lactate, calcium nitrate, calcium oxalate and calcium sulfate are disclosed as fixer agents.
Published US Patent Application 2014/0055520 discloses an ink-receiving solution comprising at least one metal salt, in particular calcium chloride.
The reaction liquids comprising a (poly)valent metal salt usually comprise a conjugate base of acids or a halide as an anion.
It is a disadvantage of the known reaction liquids that they show inferior spreading behavior on most commonly used print substrates, which makes them less suitable to be applied by in-line and off-line ink jet printing.
It is another disadvantage of the known reaction liquids that at high salt concentrations, required for enabling application of thin layers to a print substrate in order to prevent deformation of the print substrate by high liquid loading, the spreading behavior even gets worse, because commonly used surfactants lose their compatibility with the components of the reaction liquids at high salt contents.
It is therefore an object of the present invention to provide a reaction liquid comprising a metal salt content, which reaction liquid is suitable to be applied in thin layers by ink-jet printing and shows improved spreading behavior.